Alumina-supported ruthenium catalyst

ABSTRACT

A ruthenium-on-alumina catalyst including at least a ruthenium component carried by a porous α-alumina material. The catalyst has a specific surface area (S 1 ) of 7-50 m 2 /g, and a ratio S 1 /S 2  of the specific surface area of the ruthenium-on-alumina catalyst (S 1 ) to the surface area of the porous α-alumina material (S 2 ) of 3-50. The catalyst has a micropore structure having a pore diameter distribution profile in which at least one peak falls within the range of 5-1,000 angstroms. The catalyst of the invention has excellent crushing strength, and high activity per unit ruthenium weight. Moreover, the catalyst has remarkable heat resistance, maintaining its high activity even at high temperatures of reaction and firing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to ruthenium-on-alumina catalysts. Moreparticularly, the invention relates to ruthenium-on-alumina catalysts—inwhich ruthenium or similar components are carried by an α-alumina porousmaterial—which are advantageously used in a variety of a hydrogenproduction processes, inter alia, in processes making use of a steamreforming process applied to light hydrocarbons and oxygen-containingcompounds for producing synthetic gas, reduction gas suitable for use indirect-reduction iron making, city gas, and hydrogen gas. Theruthenium-on-alumina catalysts of the present invention are alsoadvantageously used in a reformer (for producing hydrogen) contained ina fuel cell.

2. Background Art

In conventional steam reforming or like processes for light hydrocarbonsby use of a catalyst, there have generally been used catalysts formed ofa transition metal such as nickel carried by a catalyst carrier such asγ-alumina.

In current steam reforming processes, in order to economize constructioncosts and operation costs, heat flux tends to be raised, whereassteam/carbon ratio (S/C) tends to be decreased. Under such operationconditions, carbon easily precipitates on the catalyst, to cause anincreased pressure difference in piping. As a result, the catalyst tubesometimes clogs to make continuing the reaction difficult. Thus, thereis strong demand for a catalyst with which the amount of carbongenerating on the catalyst is greatly suppressed as compared with thatattained by conventional catalysts, while exhibiting high catalyticactivities.

Ruthenium-on-alumina catalysts containing ruthenium as a catalyticcomponent have become of interest as catalysts which permit suppressedcarbon precipitation thereon and which have enhanced activities. Sinceruthenium-on-alumina catalysts exhibit excellent catalytic performanceas proven by their high activities and ability to suppress precipitationof carbon even under conditions of a low steam/carbon ratio duringoperation, Japanese Patent Application Laid-Open (kokai) No. 5-220397,among others, discloses ruthenium-on-alumina catalysts in whichzirconium oxide derived from a precursor zirconia sol and a rutheniumcomponent are carried by aluminum oxide containing alkaline earth metalaluminate.

However, the ruthenium-on-alumina catalysts disclosed in the abovereference has the problem that their activities are insufficient underreforming conditions of a low steam/carbon (S/C) ratio of 2 or less andat a high temperature of not less than 680° C. Also, since ruthenium isa noble metal of high price, making ruthenium-containing catalystsindustrially useful requires, in addition to securing satisfactorycatalytic performance, the suppression of ruthenium content so as toreduce catalyst costs. Moreover, in view that steam reforming reactionsare performed at high temperature, there is sought development ofcatalysts that not only have high activities, but are also resistant toheat.

From the point of prevention of environmental destruction caused by airpollution, hydrogen fuels have become of interest as alternate energysources in place of gasoline, etc. The hydrogen fuels are converted intoelectric energy by, for example, a fuel cell. Hydrogen which serves asthe starting material is generally produced from hydrocarbons oroxygen-containing compounds through a steam reforming process. Inparticular, in place of hydrocarbons such as city gas and LPG which haveconventionally been used in fuel cells, oxygen-containing compounds suchas methanol and dimethyl ether have recently come to be expected toserve as fuel for transportation power sources (electric cars). As acatalyst for reforming oxygen-containing compounds, there has been usedruthenium, nickel, or a similar metal carried by (or impregnated in) acatalyst carrier such as alumina.

A typical fuel cell generally contains a reactor for reformation. Inrecent years, reformation reactors in the form of a plurality ofconcentric hollow cylinders have acquired popularity, in which catalystlayers are arranged to form cylindrical shells so as to make theentirety of the fuel cell compact and to improve its performance(Japanese Patent Application Laid-Open (kokai) Nos. 3-122001 and60-264303).

In reformation reactors of the above type, a burner is placed at thecenter of the innermost shell and a plurality of catalyst layers aredisposed so as to surround the burner, to thereby maximize the area ofheat transfer surface and reduce the size of the reactor. Therefore, atthe time of starting up and stopping the operation of the reactor, thetemperature of the inside of a catalyst layer differ greatly from thatof the outside of the catalyst layer. The temperature difference inducesstrain in the circumferencial direction of each shell due to differencein thermal expansion, applying on catalyst layers a compression forcewhich may crush the catalyst under pressure. When the catalyst iscrushed, powder generates and clogs catalyst layers and downstreampiping, and as a result, operation may be discontinued due to elevatedflow resistance.

As a measure for preventing destruction of catalyst under pressure,“Fuel Association Journal,” Vol. 68, No. 3 (1989) discloses from pages236 to 243 a ruthenium-on-alumina catalyst in which ruthenium serves asa catalyst and α-alumina serves as a catalyst carrier.

However, since the ruthenium-on-alumina catalyst disclosed in thisjournal uses α-alumina prepared by firing γ-alumina at 1300° C., themolded α-alumina has an insufficient crushing strength for use inmulti-shell-type reformation reactors, as they require high crushingstrength. Moreover, since ruthenium is carried by α-alumina obtained byfiring γ-alumina, the resultant catalyst has a specific surface area ofas small as 6.6 m²/g, and therefore, even when ruthenium of highactivity is used as an active component, ruthenium cannot besufficiently dispersed on and within the carrier, and as a result, onlyinsufficient catalyst activity can be obtained. Furthermore, whenα-alumina is prepared through firing at a sufficiently high temperatureso as to increase the crushing strength, the resultant α-alumina of aclosest packing structure is generally not suitable as a catalystcarrier, because it does not have micropores of a submicron or smallersize, and in addition, has only a small specific surface area even whenit is molded into a catalyst carrier. In other words, when a catalystcarrier constructed of α-alumina is impregnated with an activecomponent, the specific surface area necessary for satisfactorilydispersing active components on and within the carrier is insufficient,and thus, even though the amount of the catalyst component is increased,sufficient activity cannot be obtained.

Also, as described above, Japanese Patent Application Laid-Open (Kokai)No. 5-220397 discloses a ruthenium-on-alumina catalyst in whichzirconium oxide derived from a precursor zirconia sol and a rutheniumcomponent are carried by aluminum oxide containing alkaline earth metalaluminate.

However, in consideration that the zirconia sol used in that publicationis present in the form of particles of 100 angstroms or more, thezirconium oxide derived therefrom is considered to grow into largeparticles. Moreover, since the alkaline earth metal aluminate is presentas crystals, particles thereof are also considered to grow into largeparticles. Thus, the catalyst is predicted to have disadvantages ofreduced specific surface area and insufficient catalytic activities.

SUMMARY OF THE INVENTION

The present invention was accomplished in view of the aforementionedproblems, and the object of the invention is to provide aruthenium-on-alumina catalyst—in which a porous alumina material whichis useful as a catalyst carrier due to its excellent heat resistance andcrushing strength is impregnated with an active component,ruthenium—which has a number of notable features: remarkably excellentactivity, particularly reformation activity, per unit weight ofruthenium; excellent resistance to heat which assures high activity inreactions at high temperatures: and a prolonged service life.

The above object is achieved by a ruthenium-on-alumina catalystcomprising at least a ruthenium component carried by a porous α-aluminamaterial, which catalyst has a specific surface area (S₁) of 8-50 m²/g.

In a preferred mode of the invention, the ratio S₁/S₂ of the specificsurface area of the aforementioned ruthenium-on-alumina catalyst (S₁) tothe surface area of the porous α-alumina material (S₂) is 3-50.

In another preferred mode of the invention, the ruthenium-on-aluminacatalyst has a micropore profile with at least one peak falling withinthe range of 5-1,000 angstroms.

In still another preferred mode of the invention, the porous α-aluminamaterial is impregnated with at least a ruthenium component and azirconium component, and the respective amounts (contents) are such thatthe former accounts for 0.05-5% by weight as reduced to elementalruthenium and the latter accounts for 0.05-20% by weight as reduced tozirconium oxide, both with respect to the weight of the porous α-aluminamaterial.

In still another preferred mode of the invention, the porous α-aluminamaterial is impregnated with at least a ruthenium component, a zirconiumcomponent, and an alkaline earth metal or rare earth metal component,and the respective amounts are such that the ruthenium componentaccounts for 0.05-5% by weight as reduced to elemental ruthenium, thezirconium component accounts for 0.05-20% by weight as reduced tozirconium oxide, and the alkaline earth metal or rare earth metalcomponent accounts for 0.5-20% by weight as reduced to its correspondingoxide, wherein all percentages are with respect to the weight of theporous α-alumina material.

In yet another preferred mode of the invention, the porous α-aluminamaterial is impregnated with at least a ruthenium component, a zirconiumcomponent, an alkaline earth metal or rare earth metal component, and acobalt component, and the respective amounts are such that the rutheniumcomponent accounts for 0.05-5% by weight as reduced to elementalruthenium, the zirconium component accounts for 0.05-20% by weight asreduced to zirconium oxide, the alkaline earth metal or rare earth metalcomponent accounts for 0.5-20% by weight as reduced to its correspondingoxide, wherein all percentages are with respect to the weight of theporous α-alumina material, and the cobalt component is incorporated at amolar ratio of cobalt (Co) to (Ru), Co/Ru, of 0.01-30.

Furthermore, there is provided a catalyst for steam reformationreactions applied to hydrocarbons, making use of the above-describedruthenium-on-alumina catalyst.

BEST MODE FOR CARRYING OUT THE INVENTION

Various embodiments of the ruthenium-on-alumina catalyst of the presentinvention will next be described.

I. Porous α-alumina Material

In the present invention, porous α-alumina material is used as analumina carrier. The porous α-alumina material which may be used in thepresent invention is selected from among conventional ones whosecompositions and properties have been regulated or controlled throughincorporation of additives, pretreatment, or selection of a suitablepreparation method. For example, the porous α-alumina material may besubjected to chemical treatment such as acid treatment, alkalitreatment, or ion-exchange treatment to thereby regulate its acidity;heating or firing so as to adjust the water content or the OH content inthe surface of the alumina material; or a variety of means to therebycontrol the size and distribution of micropores and the related surfacearea.

The shape and size of the porous α-alumina material of the presentinvention is not particularly limited. α-Alumina powder which serves asa starting material may be granulated, compressed, injection-molded, orsubjected to other suitable processes to form powders, granules, beads,small columns, pellets, or Raschig rings, all of which are suitably usedin the present invention. Alternatively, a carrier substrate which has aspecific structure such as a monolithic shape and is obtained frommaterials inert to chemical reaction may be spray-coated with a rawα-alumina powder to thereby form a catalyst carrier of the presentinvention.

Of these, preferred catalyst carriers are porous α-alumina materialsgranulated or molded into spheres, beads, pellets, or Raschig rings, andcoated materials formed by coating a specific structure such as amonolithic structure with α-alumina, from the viewpoint of securing asufficient specific surface area of the catalyst, reduction of pressureloss in a catalyst layer during reaction, and improving thermalconductivity to the reaction fluid. Of these types of materials,spheres, beads, Raschig rings, and coated monolithic carrier substratesare particularly preferred in consideration of high compressivestrength.

Physical properties and manufacturing methods of the porous α-aluminamaterial used in the present invention will next be described.

1. Physical Properties of Porous α-alumina Material

The porous α-alumina material used in the present invention preferablyhas the following physical properties.

(1) Micropore Volume

A preferable micropore volume of the porous α-alumina material istypically 0.05-0.5 cc/g, more preferably 0.1-0.4 cc/g, and mostpreferably 0.1-0.3 cc/g. If the volume is less than 0.05 cc/g, α-aluminaabsorbs too small an amount of liquid; i.e., it cannot sufficientlyabsorb a below-mentioned impregnation solution containing an activecatalyst component. As a result, catalyst components may be incorporatedinto a carrier only in insufficient amounts. On the other hand,micropore volumes of more than 0.5 cc/g—which indicate incompletesintering of α-alumina—may result in insufficient crushing strength.

(2) Average Micropore Size

A preferable micropore size of the porous α-alumina material istypically 0.01-100 μm, preferably 0.05-50 μm, more preferably 0.1-10 μm.When the size is in excess of 100 μm, the carrier cannot retain animpregnation solution during the below-described step for impregnatingthe carrier with an active catalyst component, and therefore, not onlyrepeated impregnation operations are required but also poor operationefficiency results. On the other hand, when the size is less than 0.01μm, a starting material hydrocarbon cannot easily diffuse intomicropores in the catalyst during reaction. In this case, there may notbe obtained catalytic activity commensurate with the amount of theactive catalyst component carried by the porous α-alumina material.

(3) Specific Surface Area

In order to increase the specific surface area of a catalyst formed byincorporating an active component into a porous α-alumina material, theporous α-alumina material per se preferably has a larger surface area.However, generally speaking, mechanical strength tends to decrease withincreasing specific surface area of α-alumina. In the present invention,the surface area of the α-alumina carrier per se is typically 0.05 m²/gor more, preferably 0.1-3 m²/g, and more preferably 0.2-1 m²/g.

(4) Crushing Strength

The crushing strength of the porous α-alumina material is typically 20kgf or more, preferably 20-100 kgf, and more preferably 40-100 kgf, asmeasured by a Kiya's crushing strength measuring apparatus. When acarrier having a strength of 20 kgf or less is used, the catalyst maycrushing during use in reactions, especially during the reactor isheated or cooled, whereas even when the strength is in excess of 100kgf, technical advantages commensurate with the strength cannot beobtained.

(5) Crystallinity

The crystallinity of the porous α-alumina material is generally 70% ormore, preferably 90% or more, more preferably 95% or more. When thecrystallinity of a porous α-alumina material is less than 70%, theporous material per se or a catalyst product obtained therefrom exhibitslow crushing strength, permitting generation of finely-divided powder inthe reactor during use in reaction. When the porous α-alumina materialis subjected to X-ray diffraction analysis, the ratio I_(B)/I_(A) of the“most intensive peak strength attributed to compounds other thanα-alumina” (I_(B)) to the “most intensive peak strength attributed toα-alumina” (I_(A)) is preferably 0.1 or less, more preferably 0.01 orless, wherein the compounds other than α-alumina include γ-alumina,η-alumina, and β-alumina. When the peak intensity ratio (I_(B)/I_(A)) isgreater than 0.1, catalytic activity of a catalyst prepared from theporous α-alumina material tends to be low.

2. Method for Manufacturing Porous α-alumina Material

(1) Starting Powder Material

The porous α-alumina material which is used in the present invention ismanufactured through granulating or shaping, and subsequently sintering,a starting material, α-alumina powder.

The grain size of the starting powder material is preferably 0.01-100μm, more preferably 0.05-50 μm, and most preferably 0.1-10 μm.

When the grain size is less than 0.01 μm, the micropore size ormicropore volume which is required for a catalyst may not always beobtained, whereas when the grain size is in excess of 100 μm, grainscannot be easily sintered and therefore a porous material having asufficient mechanical strength cannot be obtained.

(2) Additives

A variety of additives are usually mixed with α-alumina powder so as toaccelerate the sintering reaction or to form pores. Examples of theadditives include inorganic additives such as clay minerals and waterglass; and organic additives such as different types of starch grains(corn, wheat, adder's tongue lily, and potato), polyethylene glycol, PVA(polyvinyl alcohol), MC (methylcellulose), CMC (carboxymethylcellulose),glycerin, sorbitol, urea, acrylic emulsions, and waxes. Examples of theclay minerals include kaolin, bentonite, and gairome clay.

When the additive is an inorganic material, the grain size of theadditive is preferably 0.01-100 μm, more preferably 0.05-50 μm, and mostpreferably 0.1-10 μm.

The additives are preferably incorporated in an amount of less than 50parts by weight, more preferably in amounts of less than 20 parts byweight, based on 100 parts by weight of α-alumina.

(3) Molding Method

The porous α-alumina material of the present invention can generally beobtained through different molding methods by use of raw powdermaterials containing a variety of additives. There is no limitation onthe molding method, and examples of the method include press molding,rolling-granulation, wet injection molding, CIP molding, pelletizing,and powder injection molding. Alternatively, porous α-alumina materialof the present invention may be obtained through spray-coating aseparately manufactured monolithic structure.

The molded product is classified as needed and is fired in, for example,a gas furnace of 1,100-1,600° C. in order to provide the end product,porous α-alumina material of the present invention.

II. Metal Components (Components Carried by the α-alumina Carrier)

In the present invention, a ruthenium component—which has proven toexhibit high activity at least in reformation reactions—is incorporatedinto the above-described α-alumina carrier. Multi-component systemcatalysts which also contain other components described below areindustrially preferred in view of enhanced catalytic activity and anensured long service life. Incorporation of such “other components” alsoreduces the amount of ruthenium—which is expensive as it is a noblemetal—to thereby reduce the unit cost for manufacturing the catalyst.

(1) Two-component System (Ruthenium and Zirconium)

In a preferred mode of the present invention, there is provided acatalyst containing a ruthenium component and a zirconium component asthe two main metal components.

When these two metal components are incorporated into an aluminacarrier, zirconium oxide is present in the form of very fine particles,and therefore, the resultant catalyst comes to have a significantlyextended surface area. As a result, the catalyst exhibits high activityand excellent heat resistance.

The amount of respective metal components may be suitably selected inaccordance with relevant factors and conditions including properties ofthe carrier (such as the type, surface area, etc.) or use of thecatalyst (i.e., the type and property of the reaction of interest). Forexample, the amount of the ruthenium component used in the presentinvention is typically 0.05-5% by weight, preferably 0.05-2% by weight,more preferably 0.1-2% by weight (calculated in terms of metallicruthenium) with respect to the weight of the carrier. The amount of thezirconium component is typically 0.05-20% by weight, preferably 0.1-15%by weight, and more preferably 1.0-15% by weight (calculated in terms ofzirconium oxide) with respect to the weight of the carrier.

(2) Three-component System (Ruthenium, Zirconium, and Alkaline EarthMetal or Rare Earth Metal)

In the present invention, in addition to the ruthenium component andzirconium component, one or more components selected from alkaline earthmetal components and rare earth metal components may be incorporatedinto the carrier. Examples of the alkaline earth metal components andrare earth metal components include beryllium (Be), magnesium (Mg),calcium (Ca), strontium (Sr), barium (Ba), yttrium (Y), lanthanum (La),cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm),samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium(Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), andlutetium (Lu). Of these, magnesium is preferred in view of its notableeffect of enhancing the heat resistance of the zirconium component. Thetotal amount of these components is typically 0.5-20% by weight,preferably 0.5-15% by weight, more preferably 1-10% by weight,calculated in terms of the corresponding oxides of the alkaline earthmetal component or rare earth metal component.

A description will next be given of catalysts incorporating a magnesiumcomponent, which is taken as a representative example among alkalineearth metal components and rare earth metal components.

In this case, ruthenium, zirconium, and magnesium are incorporated asthe three primary components.

In a catalyst in which these three metal components are incorporatedinto an alumina carrier, zirconium and magnesium are present in the formof very fine grains of zirconium oxide and magnesium oxide,respectively. These two substances interact to suppress formation ofcrystals and grain growth. As a result, the catalyst comes to have aremarkably increased surface area, thereby providing high catalyticactivity and excellent heat resistance.

The amount of the metal components used in the present invention may besuitably selected in consideration of the aforementioned conditions. Forexample, the amount of the ruthenium component with respect to theweight of the carrier is typically 0.05-5% by weight, preferably 0.05-2%by weight, more preferably 0.1-2% by weight, calculated in terms ofmetallic ruthenium. The amount of the zirconium component is typically0.05-20% by weight, preferably 0.1-15% by weight, more preferably1.0-15% by weight, calculated in terms of zirconium oxide. The amount ofthe magnesium component is typically 0.5-20% by weight, preferably0.5-15% by weight, calculated in terms of magnesium oxide. When theamount of the magnesium component is less than 0.5% by weight, thecatalytic activity may be low.

The molar ratio of the magnesium component to the zirconium componentcontained in a catalyst, Mg/Zr, is typically 0.1-10, preferably 0.5-5,and more preferably 1-2, wherein the ratio Mg/Zr represents the molarratio of magnesium atoms (Mg) to zirconium atoms (Zr). When the molarratio Mg/Zr is less than 0.1, the incorporated components' effect ofsuppressing a decrease of the surface area is not fully exerted, and theeffect of increasing the heat resistance may become insufficient. On theother hand, even when the molar ratio is in excess of 10, improvement ofheat resistance may not be commensurate.

In the present invention, in order to further enhance the activity ofthe catalyst, a cobalt component as described below is preferablyincorporated.

(3) Four-component System (Ruthenium, Zirconium, Alkaline Earth Metal orRare Earth Metal, and Cobalt)

The amount of the cobalt component, which is an optional component inthe present invention, is typically such that the molar ratio (Co/Ru) ofcobalt (Co) to ruthenium (Ru) is 0.01-30, preferably 0.1-30, morepreferably 0.1-10. When the molar ratio is less than 0.01, the cobaltcontent decreases, and as a result, the expected effect of enhancing theactivity may not be attained. On the other hand, when the molar ratio isin excess of 30, the relative ruthenium content decreases. In this case,it is difficult to maintain the high activity of a ruthenium-containingsteam reforming catalyst applicable to hydrocarbons. Moreover, theeffect of inhibiting precipitation of carbon may be impeded even underoperation conditions of a low steam/carbon ratio.

III. Specific Surface Area of a Catalyst

In the present invention, a catalyst having a remarkably increasedspecific surface area can be obtained by impregnating a porous α-aluminamaterial with specific metal components. This is because the respectivemetal components are present as very fine grains, and yet they do notclog micropores of the porous α-alumina material.

Moreover, the catalyst of the present invention exhibits not only highcatalytic activity but also high mechanical strength and heatresistance, which are characteristics of α-alumina.

The specific surface area of the catalyst of the present invention istypically 7-50 m²/g, preferably 8-20 m²/g, more preferably 8-15 m²/g.Specific surfaces areas of less than 7 m²/g cannot provide satisfactorycatalytic activity, because the metal components cannot be dispersedextensively on and within the carrier. On the other hand, specificsurface areas in excess of 50 m²/g exhibit too small a micropore size,thus hindering diffusion of raw materials into the micropores. In thiscase, the increased specific surface area may provide no effect.

The ratio S_(1/)S₂ of the specific surface area of the catalyst of thepresent invention (S₁) to the specific surface area of a porousα-alumina material serving as a carrier (S₂) is preferably 3 or more,more preferably 5-50, particularly preferably 10-30. When the ratio isless than 3, a catalyst having a specific surface area sufficient forexhibiting satisfactory catalytic activity may not be obtained.

IV. Peak in the Micropore Distribution Profile of a Catalyst

The catalyst of the present invention has micropores. The distributionprofile of the catalyst is such that at least one peak falls within therange of 5-1000 angstroms, preferably 10-100 angstroms. The microporesare formed by the components carried on the porous alumina material. Thedistribution of micropores is computed by use of the adsorption amountof nitrogen calculated from absorption-desorption characteristics ofnitrogen under different pressures. The absence of a peak in a range ofless than 1000 angstroms in the micropore diameter distributionindicates that satisfactory micropores have not been formed: thespecific surface area is insufficient, so active components are notsufficiently distributed on the carrier, resulting in a decreasedreaction activity. However, when there is a peak within a range of lessthan 5 angstroms, the micropores are excessively small and impede theentrance of the reactive substance into the micropores, resulting inlack of the effect of improving activity.

V. Incorporation of Metal Components into a Porous α-alumina Material

1. Method of Incorporation

In the present invention, the method of incorporating a metal componentinto a porous α-alumina material is not particularly limited. Forexample, the aforementioned porous α-alumina material may be impregnatedwith a solution containing at least one or more ruthenium compounds andoptionally containing one or more zirconium compounds, one or morecompounds selected from alkaline earth metal compounds and rare earthmetal compounds (e.g., one or more magnesium compounds), and furtheroptionally, one or more cobalt compounds. In such a method, a rutheniumcomponent and optional components such as a zirconium component, alkaliearth metal component, a rare earth metal component, and a cobaltcomponent can be deposited uniformly on the surface of the porousα-alumina material or incorporated into the micropores of the porousα-alumina material, with excellent distribution. Moreover, even whentypical pretreatment such as firing at high temperature and reduction isperformed, the ruthenium component and zirconium oxide retain awell-dispersed state, easily providing a ruthenium-bearing catalyst ofhigh performance.

(1) Solution

The pH of a solution containing the metal compounds employed in theabove incorporation method is preferably adjusted to 3 or less, morepreferably 1.5 or less, through addition of an acid, etc. If the pH ofthe solution is in excess of 3, one or more the compounds contained inthe solution tend to precipitate or coagulate to form a gel, and as aresult, the metal component(s) cannot be retained on the carrier in awell-dispersed state. By contrast, when the pH is 3 or less, it isspeculated that the ruthenium compound reacts with the zirconiumcompound, etc. to form a complex-like compound, which is alsoincorporated as formed, so as to provide a catalyst having furtherimproved catalytic activity.

Moreover, a catalyst containing additives in the form of an alkalineearth metal or rare earth metal component in addition to the rutheniumcomponent and the zirconium component has a specific surface area whichis remarkably stable to heat. This heat stability is maintained duringpost-firing reactions or reactions at high temperature. Thus, thecatalyst exhibits long-term heat resistance.

(2) Solvent

No particular limitation is imposed on the solvent used in the abovesolution, and there may be used any solvent that can dissolve at least aruthenium compound and the optional compounds, i.e., a zirconiumcompound, an alkaline earth metal component or a rare earth metalcomponent, and a cobalt compound. Examples of the solvent include water,a water-based solvent, and an organic solvent such as alcohol and ether.Of these, water or a water-based solvent is preferred in view of theabove compounds' high solubility therein.

(3) Raw Materials of Metal Components

The type and shape of the compounds which serve as the startingmaterials of metal components are not particularly limited so long asthe compounds can dissolve in the above- mentioned solvents. Examples ofthe starting compounds are as follows.

(3-1) Ruthenium Compounds

Examples of ruthenium compounds which may be used in the presentinvention include ruthenium halides such as ruthenium trichloride;haloruthenate salts such as potassium hexachlororuthenate; ruthenatesalts such as potassium tetraoxoruthenate; ruthenium tetraoxide; amminecomplex salts such as hexaammineruthenium trichloride; and cyano complexsalts such as potassium hexacyanoruthenate. Moreover, a compound havinglow solubility in a solvent per se may also be used as a raw material inthe present invention so long as it becomes soluble by the addition ofor in the co-presence of an acid or an acidic compound. For example,although ruthenium oxides (such as diruthenium trioxide), rutheniumhydroxides, and ruthenium oxyhalides, etc. are insoluble or slightlysoluble in water at a pH of approximately 7, they can be used in thepresent invention, because they become soluble with the addition of acidsuch as hydrochloric acid. These ruthenium compounds may be used singlyor in combination of two or more species.

Of these raw ruthenium compounds, ruthenium trichloride is particularlypreferred in that it is widely used in industry and is easily available.

(3-2) Zirconium Compounds

Examples of zirconium compounds which may be used in the presentinvention include halides such as zirconium tetrachloride or partiallyhydrolyzed products of halides; oxyhalides such as zirconyl chloride(zirconium oxychloride); oxyacid salts such as zirconyl sulfate,zirconium nitrate, and zirconyl nitrate; zirconate salts such aspotassium tetraoxozirconate and sodium hexafluorozirconate; organic acidsalts or organic coordination compounds such as zirconium acetate,zirconyl acetate, zirconyl oxalate, and potassium tetraoxalatozirconate;zirconium alkoxides; zirconium hydroxides; and zirconium complex salts.These compounds include, in addition to compounds soluble in a solventunder normal conditions (i.e., in the absence of acid), compoundssoluble in an acidic solvent containing an acid such as hydrochloricacid or an acidic compound.

Of these zirconium compounds, zirconium oxychlorides are particularlypreferred. Examples of the oxychlorides include hydrates represented byZrOCl₂.nH₂O or ZrO(OH)Cl.nH₂O and commercially available water-basedsolutions. Zirconium oxychloride is considered to form a certaincomplex-like compound with ruthenium. These zirconium compounds may beused singly or in combination of two or more species.

(3-3) Alkaline Earth Metal Compounds and Rare Earth Metal Compounds

The alkaline earth metal compounds and rare earth metal compounds whichmay be used in the present invention include nitrates, chlorides,acetates, and oxalates of alkaline earth metals and rare earth metals;as well as alkoxide compounds of these metals. Examples thereof includenitrates such as magnesium nitrate, calcium nitrate, strontium nitrate,lanthanum nitrate, and cerium nitrate; chlorides such as magnesiumchloride, calcium chloride, strontium chloride, lanthanum chloride, andcerium chloride; acetates such as magnesium acetate and calcium acetate;oxalate such as magnesium oxalate, calcium oxalate, and strontiumoxalate; and alkoxide compounds such as magnesium methoxide, magnesiumethoxide, calcium methoxide, and calcium ethoxide. These compoundsinclude those which become soluble in a solvent through addition of acidsuch as hydrochloric acid, an acidic compound, or an alcohol such asmethanol. Of these, nitrates and chlorides are preferred inconsideration of their high solubility. These compounds may be usedsingly or in combination of two or more species.

(3-4) Cobalt Compounds

The cobalt compounds which may be used in the present invention includecompounds soluble in specific solvents as well as compounds which becomesoluble after adjustment of the pH of the solvent through addition ofacid such as hydrochloric acid or an acidic compound. Examples thereofinclude cobaltous nitrate, basic cobaltous nitrate, cobalt dichloride,and hydrates thereof. Of these, cobalt nitrates and chlorides arepreferred in view of their high solubility, with cobaltous nitrate beingparticularly preferred. These cobalt compounds may be used singly or incombination of two or more species.

(4) Preparation of Solutions

(4-1) Steps for Preparing Solutions

When the above-mentioned solutions are prepared, there is no particularlimitation regarding the order and manner of adding, mixing, ordissolving respective components including solvents, rutheniumcompounds, zirconium compounds, alkaline earth metal compounds or rareearth metal compounds, cobalt compounds, and acids. For example,specific components may be added simultaneously or sequentially to asolvent or an acid-added acidic solution. Alternatively, solutions ofrespective components which have been prepared independently may bemixed. A solution containing portions of components may be prepared, andsubsequently the remaining components may be added thereto. Although thesolution preferably measures around room temperature, it may be heatedto approximately 80° C. when accelerated dissolution is desired.

Inorganic acids (such as hydrochloric acid, sulfuric acid, and nitricacid) and organic acids (such as acetic acid and oxalic acid) may beused to enhance solubility of raw compounds in a solvent and to adjustthe pH of the solution.

(4-2) Amount of Metal Components to be Incorporated

When zirconia which also serves as a catalyst component is used incombination with ruthenium, the ratio of the zirconium compound to theruthenium compound as represented by the molar ratio (Zr/Ru) ofzirconium (Zr) to ruthenium (Ru) is 100 or less, preferably 1-50, morepreferably 2-20. When the molar ratio Zr/Ru is less than 1, thedispersion state of the ruthenium component on the carrier may becomepoor, or the ruthenium component may not be retained in the vicinity ofthe zirconium component. The reason for this is considered that portionsof the ruthenium compound cannot form a complex-like compound. On theother hand, when the molar ratio Zr/Ru is in excess of 100, thedispersion state of the ruthenium component on and within the carrier isno longer improved, and what is worse, the ruthenium component iscovered with the zirconia component, to thereby reduce the catalyticactivity due to less amounts of the ruthenium component exposed to thecarrier surface. In addition, excellent characteristics of porousα-alumina material may be marred.

When an alkaline earth metal compound or a rare earth metal compound isused in combination, the molar ratio represented by M/Zr of an alkalineearth metal or a rare earth metal (M) to zirconium (Zr) is typically0.01-10, preferably 0.05-5, more preferably 0.1-5. When the molar ratio(M/Zr) is less than 0.01, the addition of the alkaline earth metalcompound or a rare earth metal compound does not effect as expected.Namely, specific surface area of the catalyst may decrease and heatresistance of the carrier may not increase when the catalysts is exposedto high temperatures during reaction or firing. On the other hand, evenif the molar ratio M/Zr is in excess of 10, improvement of heatresistance may not be commensurate.

In cases in which a cobalt compound is used in combination, the cobaltcompound is typically used in a molar ratio (Co/Ru) of cobalt (Co) toruthenium (Ru) of 0.01-30, preferably 0.1-30, and more preferably0.1-10. When this molar ratio is less than 0.01 with low cobaltcomponent content, the expected effect of enhancing the activity may notbe attained, whereas if the molar ratio is in excess of 30, the relativeruthenium content decreases. In this case, it is difficult to maintainthe high activity as a ruthenium-containing steam reforming catalyst forhydrocarbons, and in addition, the effect to suppress precipitation ofcarbon may be lost under the operation conditions of low steam/carbonratio.

(4-3) Concentration of Each Component

No particular limitation is imposed on the quantity (concentration) ofeach compound to be dissolved in the aforementioned solution. Theconcentration of a ruthenium compound is typically selected to be 0.001mol/l or more, preferably 0.01-1 mol/l, and more preferably 0.1-0.5mol/l in terms of the molar concentration of ruthenium.

The above solution may contain, in addition to an essential rutheniumcompound, zirconium compounds, alkaline earth metal or rare earth metalcompounds, cobalt compounds, solubility-adjusting components, and othercomponents as needed, so long as the effect of the present invention isnot impeded.

(4-4) Homogeneous Dissolution In order to dissolve each compoundhomogeneously in a

solvent, the pH of the solution is adjusted to 3 or less, preferably to1.5 or less. If the pH is in excess of 3, zirconium compounds easilyhydrolyze to form hydroxide-like sol or gel. The resultant sol or gel isconsidered to have difficulty in forming the aforementioned complex-likecompound with a ruthenium component, and therefore, the addition of azirconium component may not result in enhanced dispersibility of aruthenium component.

2. Impregnation

(1) Types of Methods

Each metal component may be supported on a porous α-alumina materialthrough a conventional impregnation method by use of a solution preparedin the aforementioned manner. Examples of the process include a varietyof impregnation methods (heat-impregnation, normal temperatureimpregnation, vacuum impregnation, atmospheric pressure impregnation,impregnation-drying process, pore-filling process, arbitrarycombinations thereof, etc.), an immersion method, a light wettingmethod, a wet-adsorption method, a spray method, a coating method, andcombined methods thereof. Any method may be employed so long as itbrings a solution and a porous α-alumina material into contact so as tocarry the metal component(s) on the α-alumina material. Although asequential operation of impregnation, drying, and firing is required atleast once in the present invention, each step may optionally berepeated several times.

(2) Quantity Ratio of a Porous α-alumina Material to an ImpregnationSolution

The ratio of an alumina carrier to an impregnation solution may bedetermined in accordance with the target amount of the active metalcomponents to be carried, concentrations of metal compounds in anaqueous solution to be used, the type of impregnation method, andmicropore volume and specific surface area of the porous α-aluminamaterial to be used.

(3) Operation Conditions

No particular limitation is imposed on the conditions of impregnationprocedure. Typically, impregnation procedure is performed at atemperature ranging from ambient temperature to approximately 80° C.,preferably at room temperature or at a temperature close to roomtemperature, and under atmospheric pressure or reduced pressure (withevacuation).

(4) Drying After Impregnation

A porous α-alumina material impregnated with the aforementioned metalcomponents is subsequently dried. No particular limitation is imposed onthe drying conditions. Drying is typically performed at 50-150° C. forone hour or more, preferably at 100-120° C. for 12 hours or more. In thecase of air-drying, it is performed for about a whole day and night (24hours). Depending on the type of the impregnation method used,substantial amounts of moisture may evaporate, and a porous aluminamaterial that is already dried considerably is obtainable. In such acase, a separate drying step need not be performed.

(5) Firing After Drying

The porous α-alumina material dried as described above is thereafterfired to provide a catalyst. Firing is performed typically in air orair-flow for about 1-24 hours at 400-800° C., preferably at 450-800° C.,more preferably at 450-600° C. In a firing atmosphere, anoxygen-containing gas such as pure oxygen and oxygen-enriched air may beused totally or partially.

A catalyst product which is obtained through firing carries thereon aruthenium component, and optionally, a zirconium component, alkalineearth metal compound or rare earth metal compound, and cobalt component,and these components are typically carried in the form of oxides orcomplex oxides. The components neighbor to one another and are supportedby the porous α-alumina material in a highly dispersed state.

(6) Pretreatment

The thus-obtained catalyst may directly be used as a catalyst or acomponent in a specific catalytic reaction, or may be activated bysuitable processes of pretreatment for subsequent use in a catalyticreaction. The pretreatment may be performed by use of a customarymethod. For example, a ruthenium component may be reduced with areducing agent such as hydrogen to be converted into highly dispersedmetallic ruthenium for use in a reaction.

The reduction process by use of hydrogen is typically performed at500-850° C. until hydrogen consumption is not observed.

VI. Steam Reforming Reaction of Hydrocarbons and Oxygen-containingCompounds

A steam reforming reaction of a hydrocarbon and an oxygen-containingcompound in the presence of a ruthenium-on alumina catalyst of thepresent invention will next be described.

1. Starting Materials (Hydrocarbon, Oxygen-containing Compound, andWater)

(1) Hydrocarbon and Oxygen-containing Compound

Hydrocarbons and oxygen-containing compounds which are used in thereaction are not particularly limited. Examples of hydrocarbons includeapproximately C1-16 linear or branched saturated aliphatic hydrocarbonssuch as methane, ethane, propane, butane, pentane, hexane, heptane,octane, nonane, and decane; alicyclic saturated hydrocarbons such ascyclohexane, methylcyclohexane, and cyclooctane; and monocyclic orpolycyclic aromatic hydrocarbons. Examples of oxygen-containingcompounds (hereinafter occasionally referred to as hydrocarbons) includealcohols such as methanol and ethanol and ethers such as dimethyl etherand diethyl ether. In addition, city gas having a boiling point range of300° C. or less, LPG, naphtha, methanol for kerosene industry, andCO₂-dissolved dimethyl ether for NO_(x) reduction in combustion, etc.may be used as preferable starting materials. A mixture of two or moreof these hydrocarbons may also be used as a starting material. If thesehydrocarbons contain sulfur, they are preferably desulfurized before useto render the sulfur content about 1 ppm or less. A sulfur content ofmore than about 1 ppm may cause deactivation of catalyst. Methods ofdesulfurization are not particularly limited, and examples thereofinclude hydrogenation and adsorption.

(2) Water Content

No particular limitation is imposed on the nature of water which iscaused to react with hydrocarbons. Water may be mixed with hydrocarbonsin advance.

2. Reformation Reaction

(1) Steam/Carbon Ratio

A steam/carbon ratio in reformation reactions of hydrocarbons istypically 1.5-10, preferably 1.5-5, more preferably 2-4. When anoxygen-containing compound is used, steam can be saved on account ofoxygen originating from the compound. A hydrogen-rich gas is produced byregulating the steam/carbon ratio to fall within the above ranges. Insteam reformation using a catalyst of the present invention, carbondeposition is prevented even when the steam/carbon ratio is regulated to3 or less. Therefore, waste heat is utilized effectively.

(2) Reaction Conditions

(2-1) Reaction Temperature

Reaction temperature is typically 100-900° C., preferably 150-850° C.,more preferably 200-800° C. Raction temperature can not necessarily bepredetermined, because it depends on a variety of factors such asstarting materials which are used in the reaction.

2. Reaction Pressure

Reaction pressure is typically 0-30 kg/cm²G, preferably 0-10 kg/cm²G.

(3) Reaction Method

(3-1) Reaction Process

Either a continuous flow processor a batch process may be used, with theformer process being preferred.

In the case of a continuous flow process, a gas hourly space velocity(GHSV) of a mixture gas of hydrocarbons and steam is typically1,000-100,000 h⁻¹, preferably 2,000-50,000 h⁻¹, more preferably2,000-40,000 h⁻¹.

(3-2) Reaction Type

No particular limitation is imposed on the type of reaction or thereactor. Examples of reaction types include an immobilized bed process,a mobilized bed process, and a fluidized bed process. A tube-likereactor may be used as the reactor.

3. Reaction Product

Mixtures containing hydrogen, methane, carbon monoxide, etc. areobtained from a reaction of hydrocarbons and water in the presence of acatalyst of the present invention under the aforementioned conditions.Since these mixtures normally contain 50 vol. % or more of hydrogen, areformation process according to the present invention can be suitablyused in the manufacture of hydrogen for fuel cells.

The present invention will next be described in detail by way ofexamples.

EXAMPLE 1

α-Alumina powder having a grain size of 3-5 μm and water (in the amountof 20% by weight of the powder) were mixed by a kneader to provide amixture, which was compression-molded at 150 kgf/cm² with a moldingapparatus to provide a columnar (diameter 5 mm, height 5 mm) moldedproduct. The molded product was dried by residual heat of a firing gasfurnace and was subsequently fired in a gas furnace at 1,280° C. for 26hours to provide a porous material. This material was used as a catalystcarrier. The crushing strength of the porous material as measured by aKiya's crushing strength measuring apparatus was at least 50 kgf. InX-ray diffraction analysis, the ratio (I_(B)/I_(A)) of the mostintensive peak strength attributed to a compound other than α-alumina(I_(B)) to the most intensive peak strength attributed to α-alumina(I_(A)) was 0.001. Micropore volume and average micropore size asmeasured by the below-described method were 0.26 cc/g and 1.6 μm,respectively.

An impregnation solution was prepared by the following procedure.Ruthenium trichloride (RuCl₃.nH₂O: Ru content 38%, 0.66 g), magnesiumnitrate (Mg(NO₃)₂.6H₂O, 6.36 g), and cobalt nitrate (Co(NO₃).6H₂O, 2.47g) were dissolved in a zirconium oxychloride (ZrO(OH)Cl) aqueoussolution (ZC-2: product of Dai-ichi Rare Element Industry Co.) toprovide a solution having a total volume of 10 cc. After being stirredfor at least 1 hour, the solution was used for impregnation. Theimpregnation solution had a red-orange color and pH of 0.5 or less. Theimpregnation solution was impregnated into 50 g of the aforementionedporous α-alumina material by a pore-filling method.

The color of the as-impregnated carrier was orange, whereas it turned togreen after 5 hours' drying at 120° C. Finally, the impregnated carrierwas fired at 500° C. for 2 hours in air to provide a catalyst. Acompositional analysis revealed that the proportions of the metalcomponents of the obtained catalyst were as follows: ZrO₂ 5.0% byweight, MgO 2.0% by weight, Ru 0.5% by weight, and Co 1.0% by weight.

Physical properties of the porous α-alumina material and the catalystwere measured by the following method.

Micropore volume and an average micropore size were measured with thefollowing micropore distribution measurement apparatus (mercuryporosimeter) which uses the mercury penetration method under thefollowing conditions.

Apparatus: Micromeritics: Autopore 9220

Conditions: A catalyst was dried for at least 1 hour, followed bypenetration of mercury into the catalyst at an elevated pressure of50,000 psia according to the operation instructions of the apparatus. Amicropore size (median diameter) at the maximum micropore volume derivedfrom total micropore volume and micropore distribution was measured asan average micropore size. The measurement results are summarized inTable 1.

Micropore distribution and BET specific surface area of a catalyst weremeasured by the following apparatus under the following conditions.

Apparatus: OMNISORP 360 manufactured by Omnitron Technology Co.

Conditions: A catalyst was crushed to classify as 16-32 mesh. Aclassified catalyst (5 g) was placed in a sample vessel, and the vesselwas set in the apparatus. The sample was evacuated to 0.1 Torr or lessand heated at 300° C. for 3 h, followed by nitrogen adsorption to 150Torr. Micropore distribution and BET specific surface area werecalculated from adsorption quantity of nitrogen on the catalyst obtainedby the desorption process. By this method, a micropore distributionprofile in the range of 2.5-2000 Å, as well as related specific surfaceareas can be calculated. The measurement results are summarized in Table1.

Reaction activity of the catalyst to steam reformation of propane wasmeasured by the following method.

A catalyst (1 cc) was charged into a quartz reactor tube (insidediameter 20 mm), followed by reduction with hydrogen stream (GHSV ofhydrogen gas: 6,000 h⁻¹) at 500° C. for 2 hours. Propane and steam wereintroduced for steam reformation under the conditions: reactiontemperature 450° C. and 550° C., GHSV of propane 6,000 h⁻¹, andsteam/carbon ratio (S/C)=3.0. The formed gases were sampled for gaschromatographic analysis. The results of analysis were used to calculateconversion of propane in accordance with the following equation. Theresults of calculation are shown in Table 2.$100 - {\frac{( {C_{3}H_{8}} ) \times 3}{\begin{matrix}{{CO} + {CO}_{2} + {CH}_{4} + {( {{C_{2}H_{4}} + {C_{2}H_{6}}} ) \times}} \\{2 + {( {{C_{3}H_{6}} + {C_{3}H_{8}}} ) \times 3}}\end{matrix}} \times 100\quad (\%)}$

EXAMPLES 2 THROUGH 14

A porous columnar α-alumina material was prepared in a similar mannerexcept that α-alumina powder having a grain size of 3-5 μm (90% byweight) and bentonite (grain size 0.5-30 μm, 10% by weight) were mixedwith water (in the amount of 20% by weight of the powder) in a kneader.The crushing strength of the porous material was at least 50 kgf. InX-ray diffraction analysis, the ratio (I_(B)/I_(A)) of the mostintensive peak strength attributed to a compound other than α-alumina(I_(B)) to the most intensive peak strength attributed to α-alumina(I_(A)) was 0.005. Micropore volume and an average micropore size were0.20 cc/g and 2.2 μm, respectively.

Catalysts of Examples 2 through 14 were prepared from the same startingcompounds so that predetermined amounts of respective elements arecarried by the α-alumina materials.

Amounts of the metal elements as obtained from a composition analysis ofthe obtained catalysts are shown in Table 1.

Physical properties and activities of the porous α-alumina materials andcatalysts were determined in a manner similar to that employed inExample 1. Steam reformation of propane was also evaluated as describedin Example 1. Catalytic activity at reaction temperatures of 400° C. and500° C. were also evaluated in Examples 3 through 14. The results of theevaluation of the reactions is described in Table 2.

TABLE 1 Specific surface area Specific (m²/g) surface Micropore Contentof catalyst component (wt. %) carrier catalyst area ratio peak Ru Co ZrOMgO (S₂) (S₁) (S₁/S₂) (Å) Example 1 0.5 1.0 5.0 2.0 0.8 13.5 16.9 35Example 2 0.5 1.0 5.0 2.0 0.4 10.4 26.0 35 Example 3 0.5 0 5.0 2.0 0.48.2 20.5 38 Example 4 0.5 0.06 5.0 2.0 0.4 8.5 21.3 38 Example 5 0.50.15 5.0 2.0 0.4 9.1 22.8 36 Example 6 0.5 0.29 5.0 2.0 0.4 9.8 24.5 34Example 7 0.5 0.58 5.0 2.0 0.4 9.2 23.0 36 Example 8 0.5 1.00 5.0 2.00.4 8.6 21.5 38 Example 9 0.5 0.15 6.1 0.2 0.4 8.1 20.3 38 Example 100.5 0.15 6.1 3.0 0.4 8.8 22.0 36 Example 11 0.5 0.15 6.1 1.0 0.4 8.220.5 38 Example 12 0.5 0.15 6.1 0.5 0.4 8.2 20.5 38 Example 13 0.5 0.156.1 2.0 0.4 8.6 21.5 36 Example 14 0.5 0.15 6.1 0.0 0.4 8.1 20.3 38Note: Ru; ruthenium, Co; cobalt, ZrO; zirconia, MgO; magnesia

TABLE 2 Conversion of propane (%) 400° C. 450° C. 500° C. 550° C.Example 1 — 25 — 94 Example 2 — 21 — 92 Example 3 2.0 12 58 84 Example 42.4 11 41 85 Example 5 4.4 22 88 93 Example 6 5.7 28 94 94 Example 7 4.623 93 91 Example 8 2.7 12 43 82 Example 9 0.8 1 8 7 Example 10 4.5 23 9291 Example 11 0.9 4 14 52 Example 12 0.3 1 3 10 Example 13 3.2 14 50 68Example 14 1.4 4 10 19

As is apparent from Tables 1 and 2, the catalyst of Example 1 and thatof Example 2 both having a large specific surface area and a microporesize of less than 1000 Å exhibited high propane conversion and catalyticactivity.

As described above, the ruthenium-on-alumina catalyst of the presentinvention having a specified porous α-alumina material as a catalystcarrier exhibits excellent crushing strength. Accordingly, the catalystof the present invention is not crushed in a reformation reactor, andprevents a catalyst layer and piping from clogging. The catalyst of thepresent invention has an enlarged specific surface area of 7-50 m²/g,which facilitates effective supporting of metal components. In acatalyst of the present invention, a ruthenium component and an optionalcobalt component and magnesium component are supported in the vicinityof a zirconium component, in a highly dispersed state and with good heatstability. When used in steam reformation of a hydrocarbon, it exhibitshigh catalytic activity per contained ruthenium component and excellentheat resistance. The high catalytic activity may be satisfactorilymaintained under high temperatures. The catalyst of the presentinvention is particularly suitable, in terms of both costs and catalyticactivity, for steam reformation in the manufacture of hydrogen for fuelcells. Thus, the catalyst has great value in industry.

What is claimed is:
 1. A ruthenium-on-alumina catalyst, comprising: aruthenium component carried by a porous α-alumina material, whichcatalyst has a specific surface area (S₁) of 7-50 m²/g, and a ratio(S₁/S₂) of the specific surface area of the ruthenium-on-aluminacatalyst (S₁) to the surface area of the porous α-alumina material (S₂)of 3-50, the catalyst being useful in steam reforming reactions ofhydrocarbon and oxygen-containing compounds.
 2. The ruthenium-on-aluminacatalyst according to claim 1, wherein the catalyst has a specificsurface area (S₁) of 8-20 m²/g, the catalyst being useful in steamreforming reactions of hydrocarbon and oxygen-containing compounds. 3.The ruthenium-on-alumina catalyst according to claim 1, wherein theporous α-alumina material is impregnated with a ruthenium component anda zirconium component, and the respective amounts are such that theruthenium component accounts for 0.05-5% by weight as reduced toelemental ruthenium and the zirconium component accounts for 0.05-20% byweight as reduced to zirconium oxide, with respect to the weight of theporous α-alumina material, the catalyst being useful in steam reformingreactions of hydrocarbon and oxygen-containing compounds.
 4. Theruthenium-on-alumina catalyst according to claim 1, wherein the porousα-alumina material is impregnated with a ruthenium component, azirconium component, and an alkaline earth metal or rare earth metalcomponent, and the respective amounts are such that the rutheniumcomponent accounts for 0.05-5% by weight as reduced to elementalruthenium, the zirconium component accounts for 0.05-20% by weight asreduced to zirconium oxide, and the alkaline earth metal or rare earthmetal component accounts for 0.5-20% by weight as reduced to itscorresponding oxide, wherein all percentages are with respect to theweight of the porous α-alumina material, the catalyst being useful insteam reforming reactions of hydrocarbon and oxygen-containingcompounds.
 5. The ruthenium-on-alumina catalyst according to claim 1,wherein the porous α-alumina material is impregnated with a rutheniumcomponent, a zirconium component, an alkaline earth metal or rare earthmetal component, and a cobalt component, and the respective amounts aresuch that the ruthenium component accounts for 0.05-5% by weight asreduced to elemental ruthenium, the zirconium component accounts for0.05-20% by weight as reduced to zirconium oxide, the alkaline earthmetal or rare earth metal component accounts for 0.5-20% by weight asreduced to its corresponding oxide, wherein all percentages are withrespect to the weight of the porous α-alumina material, and the cobaltcomponent is incorporated at a molar ratio of cobalt (Co) to (Ru), Co/Ruof 0.01-30, the catalyst being useful in steam reforming reactions ofhydrocarbon and oxygen-containing compounds.
 6. The ruthenium-on-aluminacatalyst according to claim 1, wherein the alkaline earth metal or rareearth metal component is magnesium, the catalyst being useful in steamreforming reactions of hydrocarbon and oxygen-containing compounds. 7.The ruthenium-on-alumina catalyst according to claim 1, wherein themicropore volume of the porous α-alumina material ranges from 0.05-0.5cc/g.
 8. The ruthenium-on-alumina catalyst according to claim 1, whereinthe micropore size of the porous α-alumina material ranges from 0.01-100μm.
 9. The ruthenium-on-alumina catalyst according to claim 1, whereinthe crushing strength of the porous α-alumina material ranges from20-100 kgf.